This invention pertains to improved electron emissive coatings which can be easily fabricated in miniature form for use in various electron discharge devices which are also now being introduced in smaller sizes such as photographic flash tubes and electric discharge lamps. More particularly, this invention relates to electron emissive coatings of a relatively minor thickness which can be sintered to a refractory metal substrate having various shapes and which exhibit performance characteristics fully equal or superior to the conventional electron emission means.
In U.S. Pat. No. 4,275,330, issued June 23, 1981 and assigned to the assignee of present invention, there is described electron emission means in the form of a porous sintered refractory metal body such as a sintered tungsten pellet which is impregnated with various refractory metal interoxides to provide improved resistance to deterioration in a discharge lamp operating environment. Problems exist in the fabrication of the pressed refractory metal pellets used in this type electrode which are aggravated with miniaturization of the discharge lamp device often leading to high shrinkage and lack of reproducible electrode preformance along with higher costs. Assembly of this type electrode member further entails joinder of the pressed pellet to a refractory metal shank when the discharge lamp is constructed which also leads to higher costs than would occur with a single piece electrode construction. In a still pending application, Ser. No. 39,266, filed May 16, 1979, in the names of J. C. Sobieski, J. E. Spencer, G. L. Thomas, and E. C. Zukowski, and assigned to the present assignee, there is described an all glass type flash tube using the same type electrode construction. Specifically, the cathode member in said electric discharge device can comprise a molybdenum body shank having secured thereto by conventional means a pressed sintered pellet of tantalum or some other suitable refractory metal which is impregnated with a suitable emission material for this type lamp or device operation to include barium aluminate and barium tungstate materials as well as still other known interoxides.
In a more recently filed still pending application Ser. No. 161,431, filed June 20, 1980 in the names of R. K. Datta and D. M. Speros, also assigned to the present assignee, electron emitting coatings are disclosed for use in a metal halide arc lamp which comprise a coating of the electron emission material being deposited on the cathode member having an elongated shaped body of tungsten metal which can terminate in a balled end by melting back the tungsten shank. Said one piece electrode construction employs a coating of the emission material which is deposited on the balled end of the tungsten shank as oxides of scandium and dysprosium or borides of thorium, scandium and lanthanum for improved performance in this type lamp. The cathode member in such lamp construction can further employ a tungsten helix wound about the tungsten shank and with the electron emission coating being disposed between the helix turns and the shank.
It would be generally desirable to simplify the cathode member construction for all type electric discharge devices and by means enhancing size reduction of the device itself. It would be further desirable to simplify said cathode member construction in a manner which does not sacrifice any of the desirable operating characteristics during device operation.